biosemu: include <asm/io.h> header

This makes sure we have inline functions such as inb/outb that
are used in these two files by including the arch-specific
<asm/io.h> header. However the ARM version does not provide the
accessors unless the config symbol __io is also defined so add
that in front of the include.

After this the bios emulator will compile on ARM systems.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>